Conventionally, paper feed rollers have been used for conveying paper in various fields. For example, in an image forming device such as a copying machine and a printer, a paper feeding unit is generally provided to separate and send out paper sheets one by one from a paper sheet cassette containing the paper sheets to an image forming unit. While a paper feeding unit of a pad retarding type (FR type), or of a friction retarding type (FRR type) or the like is conventionally put into practical use, one of the FRR type is often employed because of high reliability in preventing duplicate feed of the paper sheets.
The paper feeding unit of the FRR type has: a picking-up roller which comes into contact with the uppermost part of paper sheets contained in a paper sheet cassette and draws the paper sheet out of the paper sheet cassette with friction force; a feeding roller which sends out the paper sheet drawn out to a paper sheet conveying path; and a retard roller which is brought into press contact with the feeding roller and is stopped or given rotational driving force in the reverse direction to the paper sheet conveying direction via a torque limiter.
The paper feed roller often has a roller surface that undergoes emboss processing and is given a surface roughness based on the embossed surface composed of crest portions and valley portions in order to suppress sticking of paper powder and maintain a coefficient of friction for a long period of time (for example, refer to Patent Document 1).